Low numerical aperture (low-NA) solar lighting system

ABSTRACT

A low numerical aperture (low-NA) light concentration and transmission system collects, concentrates and transmits light for interior illumination. A solar tracker aligns a primary light concentrator to collect light and direct the light to a secondary light concentrator and a filter for removing ultraviolet and infrared radiation. On exiting the secondary light concentrator, the optical axis of the concentrated light is aligned to optimize the numerical aperture of the concentrated light with a numerical aperture (NA) optimizer having a light guide to direct the concentrated light to an interior luminaire. The method of the low numerical aperture transmission of light has the advantages of fewer reflections in the light guide, low loss, low cost, and easy installation and operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. ProvisionalApplication Ser. No. 61/094,117 titled “Low Numerical Aperture (Low-NA)Solar Lighting System” filed Sep. 4, 2008, which is hereby incorporatedby reference. This application also claims the benefit of priority ofU.S. Provisional Application Ser. No. 61/094,113 titled “One-axistracking concentrating photovoltaic and solar hot water hybrid system”filed Sep. 4, 2008, which is hereby incorporated by reference. Thisapplication also claims the benefit of priority of U.S. ProvisionalApplication Ser. No. 61/094,115 titled “Alternating current electricitygeneration from concentrated sunlight” filed Sep. 4, 2008, which ishereby incorporated by reference. This application also claims thebenefit of priority of U.S. Provisional Application Ser. No. 61/094,120titled “Solar lighting system with one-axis tracking” filed Sep. 4,2008, which is hereby incorporated by reference. This application isrelated to co-pending U.S. patent application Ser. No. 12/584,050 titled“CONCENTRATED PHOTOVOLTAIC AND SOLAR HEATING SYSTEM” filed Aug. 27,2009, and to co-pending U.S. patent application Ser. No. 12/584,051titled “GENERATING ALTERNATING CURRENT FROM CONCENTRATED SUNLIGHT” filedAug. 27, 2009, both of which are incorporated by reference.

BACKGROUND

1. Field of Invention

This invention relates to the field of solar energy and lighting, andmore specifically to using natural light for interior lighting.

2. Related Art

The transmission of concentrated solar energy via a light guide providesflexible options for numerous applications of solar lighting, solarheating, solar cooking, solar electric power generation, and photophysical and photochemical processes. Interior daylight lighting systemsinclude windows and skylights, tubular solar lighting devices, and fiberoptic solar lighting.

Fundamental problems remain, however, that keep solar lightingtechnology from widespread acceptance. Windows and skylight are limitedby the shape and orientation of the building design. Solar light tubessuffer an extensive loss from collection and transmission limitations.Large diameter tubes are required because the light tube inlet islimited to collecting the solar light coming through its cross-section.Thereafter, the combined effect of multiple reflections along the lengthof the tube, with each reflection suffering a 5% to 15% reflection loss,diminishes the amount of light available at the outlet to less than 8%after a conservative 50 reflections in a solar light tube. Fiber opticbundles, while losing less light than solar tubes, are very expensivefor general lighting applications.

SUMMARY OF THE INVENTION

Systems and methods provide for using natural light including sunlightand moonlight for optimized interior lighting. Incoming natural light isconcentrated and then optimized to provide a greater luminosity thanwithout optimization. The method of optimization aligns the concentratedsunlight to a low numerical aperture within the thermodynamic range toreduce the number of loss-inducing reflections through the light guide.

Some embodiments provide for using different concentrator systems, whichmay be a combination parabolic-hyperboloidal concentrator system, acombination parabolic-hyperboloidal concentrator with light guidesystem, a combination Fresnel lens and negative lens concentratorsystem, or a combination Fresnel lens and fiber optic bundleconcentrator systems.

Other embodiments provide for a solar tracking system of one or multipleaxis to allow for a moving light source, such as the sun or moon.Another embodiment further includes filtering the ultraviolet andinfrared radiation. Some embodiments may include a horizontal orvertical light guide for redirecting the concentrated and low-NAoptimized light to an interior lighting fixture.

These embodiments may be used in various configurations of aconcentrator system, a tracking system, a radiation filter system, and alight guide system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of the low numerical aperture lightingsystem.

FIG. 2 shows an embodiment of the natural light collector andconcentrator for the low numerical aperture (low-NA) lighting system.

FIG. 3 shows an embodiment of the low numerical aperture (low-NA)optimizer for the low numerical aperture lighting system.

FIG. 4 shows an alternate embodiment of the low numerical aperture(low-NA) optimizer for the low numerical aperture lighting system.

FIG. 5 shows a different embodiment of the low numerical aperture(low-NA) optimizer for the low numerical aperture (low-NA) lightingsystem.

FIG. 6 shows another embodiment of the low numerical aperture (low-NA)optimizer for the low numerical (low-NA) aperture lighting system.

FIG. 7 shows an alternate embodiment of the low-NA lighting system.

FIG. 8 shows a different embodiment of the low-NA lighting system.

FIG. 9 shows another embodiment of the low-NA lighting system.

FIG. 10 shows a different embodiment of the low-NA lighting system.

FIG. 11 shows an embodiment of the low-NA lighting system.

FIG. 12 shows an embodiment of the one-axis low-NA lighting system

FIG. 13 shows an alternative embodiment of the one-axis low-NA lightingsystem.

FIG. 14 shows expanded views of a compound parabolic secondaryconcentrator.

FIG. 15 shows a flowchart of a method for concentrating natural lightfor interior lighting.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an embodiment of the low numerical aperture (low-NA)lighting system. The system may comprise a primary light concentrator105, a secondary light concentrator 110, concentrated light 115, anaperture 120, a light source tracker 125, a low numerical apertureoptimizer 130 and a light fixture 135.

The numerical aperture (NA) characterizes an optical system as afunction of the index of refraction (n) of the medium around a collector(n=1.0 for air, n=1.33 for pure water, and up to 1.56 for oils), and theangular width (theta) of the light source with respect to the collector.Solar illuminator systems collect sunlight at one location and guide thelight to a light fixture at the other end of the guide. Equation 1algebraically characterizes the range of angles over which the systemcan accept or emit light.NA=n*sin(theta)  Equation 1

Theta represents the half-angle of the maximum cone of the light source,e.g., the sun. For a non-concentrating collector focused on the sun, themaximum value of theta is 0.27. To increase the amount of capturedsunlight, solar illuminators use concentrators. There is a thermodynamiclimit, however, to how small the NA can be. Equation 2 describes thislimit.sin(theta)>sin(0.27)*(D/d)  Equation 2

As shown in FIG. 1, the primary light concentrator 105 has an insidecollector diameter (“D”), while the low numerical aperture optimizer 130has an inside diameter (“d”).

In actuality, natural light illuminators suffer losses between theprimary collector and the illuminator fixture. The factors affectingthese losses include the designed transmission efficiency (h<1), thereflectivity of the light guide (r<1, often 0.90 to 0.999) and the lightguide length (L). Equation 3 describes the net natural light transmittedby a solar illuminator of this configuration.tan(theta)=<|ln h/ln r|*(d/L)  Equation 3

In the present invention, incoming light enters the primary lightconcentrator 105. In some embodiments, the incoming light may besunlight or reflected sunlight such as moonlight. In some embodiments,artificial light may be used. The primary light concentrator 105concentrates the incoming light by directing the incoming light strikingthe primary light concentrator 105 toward a common focal point. At thecommon focal point is the secondary light concentrator 110, whichreceives the concentrated incoming light from the primary lightconcentrator 105. Although the secondary light concentrator 110 does notcollimate the light, the secondary light concentrator 110 keeps theconcentrated sunlight convergent and directs it toward aperture 120. Theconcentrated light 115 then exits the primary light concentrator 105 viaaperture 120.

Tracking the light source is light source tracker 125, which isconnected to the primary light concentrator 105 to assure that theprimary light concentrator 105 is optimally oriented at all times towardthe light source. In one embodiment, the light source tracker 125monitors both the azimuth and elevation of the natural light source andwith a dual axis motor system, continuously aligns the primary lightconcentrator 105 to directly face the natural light source. In someembodiments, the light source tracker 125 may be single axis system.Other embodiments may simply track the natural light source withoutaligning the primary light concentrator 105, or omit the light sourcetracker 125.

After passing through aperture 120, the concentrated light 115 enters alow numerical aperture optimizer 130 which has a diameter “d” and length“L” and which is described in greater detail in FIG. 3. In someembodiments, the low numerical aperture optimizer 130 is cylindricallyshaped. The low numerical aperture optimizer may be shaped differentlyin other embodiments. On entering the low numerical aperture optimizer130, the concentrated light 115 is optimized to a low-NA according toEquation 3 to provide the best lighting possible. On passing through thelow numerical aperture optimizer 130, the low-NA light 115 enters thelighting fixture 135 and illuminates the adjacent area.

FIG. 2 shows an embodiment of the natural light collector andconcentrator for the low numerical aperture solar lighting system. Thenatural light collector and concentrator may comprise the primary lightconcentrator 105, the secondary light concentrator 110, the concentratedlight 115, the aperture 120, a mirror film 205, and a spectrallyselective filter 210.

In one embodiment, the primary light concentrator 105 may be a parabolicreflector dish. One example is a C-band parabolic satellite dish. Toenhance the reflectivity of the parabolic reflector dish, the innersurface of the primary light concentrator 105 may be covered with mirrorfilm 205. One example is a mirror film available under the brand nameReflecTech® (r approx. 0.94).

In some embodiments, the secondary light concentrator 110 may be ahyperboidally dish shaped positioned at the focal point of the primarylight concentrator 105 to receive an optimum amount of the lightreflected by the primary light concentrator 105.

To improve the usefulness of the concentrated light, the secondary lightconcentrator 110 may have a spectrally selective filter 210 to filterultraviolet light and infrared light from the concentrated sunlight. Theultraviolet (UV) is removed from light due to its hazardous nature tohuman skin and furniture. The infrared (IR) is removed to reduce theheat load from sunlight, which increases the cooling cost of buildings.

Many types and brands of UV and IR filters are available. In someembodiments, a filter film such as “Energy Film®” may be applied to theprimary concentrator 105. Some filter film brands may pass over 75% ofthe visible light while blocking 97% of the UV and 70% of the solarheat. A cold mirror coating on the secondary light concentrator 110 maysuffer only 5% loss, but is likely more costly. A stand-alone hotmirror, as shown in FIG. 2 may have less or more filtering efficiencyfor a moderate price.

FIG. 3 shows an embodiment of the low numerical aperture optimizer 130for the low numerical aperture lighting system. The low-NA optimizer isan assembly of optical components to achieve optimized numericalaperture of the concentrated sunlight in the light guide. The lownumerical aperture optimizer 130 may comprise a highly reflective mirror305, a reflective mirror hinge 310, a reflective mirror controller 315,an upper light guide 320, a highly reflective film 325, a light guidemirror 330 and a lower light guide 335.

On reaching the low-NA optimizer 130, the concentrated light 115reflects off the highly reflective mirror 305. The reflective mirrorhinge 310 affixes the highly reflective mirror 305 to the low-NAoptimizer 130.

Controlling the angle of the highly reflective mirror 305 with respectto the low-NA optimizer 130 is the highly reflective mirror controller315. The highly reflective mirror controller 315 acts in coordinationwith the light source tracker 125 to assure that the concentrated light115 enters the low-NA optimizer 300 closer to an optimal angle.

On reflecting off the highly reflective mirror 305, the concentratednatural light 115 enters the low-NA optimizer 130 converging along themidline of upper light guide 320 as shown by line “Av.”

While Equation 1 describes the numerical aperture of the light as afunction of sin(theta), Equation 2 shows that the value for sin(theta)is determined as a function of the diameter of the primary lightconcentrator and the diameter of the low-NA optimizer 130. Consequently,the selected diameter of the upper light guide 320 of the low-NAoptimizer 300 depends on the size of the primary light concentrator, andthe desired efficiency of the low-NA optimizer system.

In some embodiments, the highly reflective film 325 coated inside theupper light guide 320 reflects the concentrated light 115 that is notconverging along the midline of the upper light guide 320 to the lightguide mirror 330. One example of a highly reflective film is availableunder the brand name ReflecTech® (r approx. 0.94). In some embodiments,the highly reflective film 325 may be a coating. The low-NA concentratedlight 115 may then enter the lighting fixture 135 as shown in FIG. 1 andilluminate the area.

As inferred by Equation 3, the length of the solar tube detrimentallyaffects the luminosity of the concentrated light 115 conducted to thelight fixture. The parameter L in Equation 3 equals the sum of thedistance from point E at the midpoint of the entrance of the low-NAoptimizer 130, to point F on the surface of the light guide mirror 330to point G at the end of the lower light guide 335. Consequently, longersolar tubes without the low-NA optimizer suffer larger luminositylosses.

A shortened light guide directly above the light fixture 135 as shown inFIG. 1 may not be possible. To provide for low-NA optimized lighting inthose instances, some embodiments of the present invention may comprisethe light guide mirror 330 and the lower light guide 335.

On exiting the upper light guide 320, the concentrated light 115 entersthe lower light guide 335 and strikes the light guide mirror 330. As theangle of incidence is equal to the line of reflection, the concentratedlight 115 reflects into the lower light guide 335 with the same anglealong horizontal optical axis Ah thus optimizing the concentrated light115 to a low-NA.

The lower light guide 335 may be fabricated from 0.020″ PVD coatedaluminum sheet. It is of 99.9% specular reflectivity at 60° angle(emissivity=0.03, −ASTM E 1651-94, 179-81 & 430-78). The highlyreflective aluminum sheet may be rolled into a 3″ diameter light tube.As with the upper light guide 320, the lower light guide 335 may also becoated with the highly reflective film 325. As inferred by Equations 2and 3, the r-value of the highly reflective film and the light guidediameter (d) of the low-NA optimizer 130 affect the range of numericalaperture of the concentrated light. Consequently, consistency in ther-value of the highly reflective film 325 and in the diameter of thelight guides 320 and 335 throughout the low-NA optimizer 130 affect theluminosity of the light from the lighting fixture 135. Thus, the samehighly reflective film and the same light guide diameter arepreferentially used in each light guide portion 320 and 335 on eitherside of the light guide mirror 330.

Another advantage of the present invention is that with either the sunhigh above, or low in the sky, the low-NA optimizer system delivers alow-NA concentrated light with minimized reflective losses to the lightfixture 135 (not shown). Consequently, the low-NA optimizer systemnegates the need for large diameter solar tubes prevalent in typicalsolar installations.

FIG. 4 shows an alternate embodiment 400 of the low numerical apertureoptimizer 130 for the low numerical aperture lighting system 100. Thelow numerical aperture optimizer may further comprise a second highlyreflective mirror 325, and a diverging refractive lens 410 (a.k.a. anegative lens). This embodiment may comprise the primary and secondarylight concentrator (not shown here) as shown in FIG. 1 and FIG. 2.

In some installations, the configuration of the light source, thebuilding and the primary light concentrator may be such that the low-NAoptimizer 130 is not above the lighting fixture 135. In some of theseembodiments, the alternate embodiment 400 of the low numerical apertureoptimizer may be suitable.

As shown in FIG. 4, the concentrated light 115 enters the low-NAoptimizer 400 along an optical axis “Av.” To achieve an optimal low-NAconcentrated light, there may be one or more of the highly reflectivemirrors 305 and 325 to direct the concentrated light 115 into the lightguide 335.

As the angle of incidence is equal to the angle of reflection, the lightguide mirror 330 reflects the concentrated light 115 along a lineapproximating the optical axis Ah.

On exiting the light guide mirror 330, the concentrated light 115 entersthe light guide 335 portion of the low-NA optimizer 400. The light guide335 conducts the concentrated light 115 towards the light fixture.

In typical solar tube installations, the diameter of the light guide isapproximately equal to diameter of the primary light concentrator tomaximize luminosity at the fixture. In the present invention, however, adiverging refractive lens 410 having a focal length Lf may be positionedin lower light guide 335 to optimize the low-NA concentrated light andminimize luminosity losses from reflections. This benefit of the presentinvention mitigates the losses of long light guides and the need forlarge diameter tubing. In particularly long light guides, more than onediverging refractive lens 410 may be used and properly spaced apartaccording to the focal length of the lens.

Some incoming light may be at such a low angle that it diverges from theoptical axis Ah before reaching the diverging refractive lens 410. Tominimize these losses, the lower light guide 335 may also have a highlyreflective film 325 or coating as earlier described.

FIG. 5 shows a different embodiment 500 of the low numerical apertureoptimizer 130 for the low numerical aperture lighting system 100. Thisembodiment may comprise the highly reflective mirror 305, the highlyreflective mirror hinge 310, the highly reflective mirror controller315, the solar tracker 125, a semi-circular light guide 505, and thehighly reflective film 325 (not shown). This embodiment may comprise theprimary and secondary light concentrator (not shown here) as shown inFIG. 1 and FIG. 2.

In lieu of the light guide mirror 330, the low-NA optimizer 500 has aninside coating of the highly reflective film 325 to optimize theconcentrated light 115 to a low-NA. Once again, the optical axis linesAv and Ah are perpendicular to each other, with the semi-circular lightguide 505 shaped to optimize the low numerical aperture of theconcentrated light within the thermodynamic limit.

FIG. 6 shows another embodiment 600 of the low numerical apertureoptimizer 130 for the low numerical aperture lighting system 100. Thelow numerical aperture optimizer 600 may comprise the primary andsecondary light concentrator (not shown here) as shown in FIG. 1 andFIG. 2. This embodiment may comprise the highly reflective mirror 305,connected to the highly reflective mirror controller 315, which works incoordination with solar tracker 125 to align highly reflective mirror305 so that concentrated light 115 enters the upper light guide 605properly aligned to optical axis Av. The embodiment 600 may alsocomprise the light guide mirror 330 and lower light guide 335, althoughthese are optional as described in FIG. 3.

This embodiment of the low-NA optimizer 600 differs from otherembodiments in that the upper light guide 605 may be in the shape of areverse compound parabolic concentrator (CPC) or other shape of areverse conic concentrator. The upper light guide 605 in the shape of acompound parabolic concentrator offers the advantage of orienting theincoming light to a lower numerical aperture. As with the upper lightguide 320, the upper light guide 605 may be coated on the interior withthe highly reflective film 325.

Consequently, the embodiment of the low-NA optimizer 600 deliversrelatively the same amount of light to the light fixture 135 (not shown)at the end of the lower light guide 335 as other embodiments of thelow-NA optimizer. Some embodiments of the low-NA optimizer 600 mayinclude the diverging refractive lens 410.

FIG. 7 shows an alternate embodiment 700 of the low-NA lighting system.The system 700 may comprise the primary light concentrator 105, thesecondary light concentrator 110, the concentrated light 115, the solartracker 125, a transitional light guide 705, the light source tracker125, the CPC low numerical aperture optimizer 710, and the light fixture135 (not shown). The UV and IR filter 210 as shown and described in FIG.2 is optional, and is not shown here. The embodiment 700 may alsocomprise the light guide mirror 330 and lower light guide 335, althoughthese are also optional as described in FIG. 3.

On reaching the low-NA lighting system 700, light enters the primarylight concentrator 105 and secondary light concentrator 110. Atransitional light guide 705 conducts the concentrated light 115 to theCPC low-NA optimizer 710 with little loss. Consequently, the CPC low-NAoptimizer 710 receives approximately as much light as in otherembodiments. In some embodiments, the transitional light guide 705 maybe a fiber optic bundle. In some embodiments, the transitional lightguide 705 may be a light guide as described for lower light guide 335.

The low-NA optimizer 710 is similar to the previously described low-NAoptimizers, but lacks the highly reflective mirror 305 and the highlyreflective mirror controller 310. Some embodiments of the low-NAoptimizer 710 may include the diverging refractive lens 410. Someembodiments of the low-NA optimizer system 700 may use a differentlow-NA optimizer such as embodiments 130, 400 or 500, but without thehighly reflective mirror 305 and the highly reflective mirror controller310.

FIG. 8 shows a different embodiment 800 of the low-NA lighting system.The low-NA lighting system may comprise the solar tracker 125, a Fresnellens 805, a UV and IR filter 810, the concentrated light 115, with thelow-NA optimizer 130 of FIG. 3, comprising the highly reflective mirror305, the light guide mirror 330, the lower light guide 335 and thehighly reflective film 325 coating the light guides 320 and 335. Someembodiments may comprise a diverging refractive (negative) lens 815.

On reaching the low-NA lighting system 800, light enters the Fresnellens 805, which may be used in place of the primary light concentrator105 and the secondary light concentrator 110. The solar tracker 125controls the position of the Fresnel lens 805. The Fresnel lens 805includes a substantially polygonal focusing portion adapted to focus theincoming light to the NA optimizer 130. On either side of the Fresnellens 805, a UV and IR filter 810 may be placed to filter the UV and IRradiation as described in FIG. 2. More than one Fresnel lens may beused, but they should all share the same focus point to assure the bestlow-NA optimization.

In some embodiments, as shown here, the diverging refractive (negative)lens 815 may be used between the Fresnel lens and the NA optimizer 130to modify the numerical aperture of the concentrated light beforereaching the NA optimizer 130.

The shapes and functions of the low-NA optimizer 130, comprising theupper light guide 320, the light guide mirror 330, and the lower lightguide 335 are as earlier described. Some embodiments may include thediverging refractive lens 410.

FIG. 9 shows another embodiment 900 of the low-NA optimizer system. Thesystem may comprise the solar tracker 125 controlling a plurality ofFresnel lens 805, at least one UV and IR filter 810, a plurality offiber optic bundles 905, and the low-NA optimizer 710. In thisembodiment, the plurality of Fresnel lens 805 may not have the samefocus point. Instead, the plurality of fiber optic bundles 905 transmitthe concentrated light 115 from the plurality of Fresnel lens to thelow-NA optimizer 710.

The plurality of fiber optic bundles 905 should have a large numericalaperture. Sizes of 3-mm with 30-degree accepting angle and 5-mm opticalfiber with 40-degree accepting angle have been successfully tested.Acrylic 3-mm diameter rods have also been successfully used as theplurality of fiber optic bundles 905.

The function and elements comprising the low-NA optimizer 710 aredescribed in FIG. 7. Some embodiments may include the divergingrefractive lens 410. Some embodiments of the low-NA optimizer system 900may use a different low-NA optimizer such as embodiments 130, 400 or500.

FIG. 10 shows a different embodiment 1000 of the low-NA lighting system.The low-NA lighting system 1000 may comprise the Fresnel lens 805, theconcentrated light 115, a low-NA optimizer comprising a concentratedlight collecting reflector 1005 with highly reflective film 325, anupper light guide 1010 with highly reflective film 325, a lower lightguide 1015 with highly reflective film 325, and a reflector 1020. Otherelements of the system, such as the solar tracker 125, the optional UVand IR filter 810 and the negative lens 815 may be present in theinvention, but are not shown here for simplicity.

On reaching the low-NA lighting system, light enters the solar tracker125 controlled the Fresnel lens 805, which may be used in place of theprimary light concentrator 105 and the secondary light concentrator 110.The Fresnel lens 805 includes a substantially polygonal focusing portionadapted to focus the incoming light to the reflector 1005. On eitherside of the Fresnel lens 805, the UV and IR filter 810 (not shown) maybe placed to filter the UV and IR radiation as described in FIG. 2. Morethan one Fresnel lens may be used, but they should all share the samefocus point to assure the best low-NA optimization.

The concentrated light 115 enters the concentrated light-collectingreflector 1005 of the low-NA lighting system 1000, which may be withhighly reflective film 325. In some embodiments, the concentratedlight-collecting reflector 1005 may have an open port for receiving theconcentrated light 115. In some embodiments, the concentratedlight-collecting cone 1005 may be completely transparent for receivingthe concentrated light 115. Other embodiments of the concentratedlight-collecting reflector 1005 may receive the concentrated light 115through a transparent or internally mirrored window.

The highly reflective film 325 of the concentrated light-collectingreflector 1005 reflects the concentrated light 115 into the upper lightguide 1010. The upper light guide 1010 transmits the incoming light to alow-NA along optical axis Av, and then into the lower light guide 1015with its reflector 1020. As with the other embodiments of the low-NAoptimizer, the upper light guide 1010 and the lower light guide 1015 arecoated with the highly reflective film 325.

The length, angle and diameter of the reflector 1020 are constructed toorient the concentrated light 115 to a low-NA along the optical Axis Ah,and then towards the light fixture 135 (not shown). Some embodiments ofthe low-NA lighting system 1000 may include the diverging refractivelens 410.

Embodiments of the concentrated light collecting reflector 1005 or thereflector 1020 of the low-NA lighting system 1000 may comprise a conicexponential concentrator, a reverse conic parabolic concentrator, areverse conic exponential concentrator, a parabolic reflector or anelliptical reflector.

FIG. 11 shows an alternative embodiment 1100 of the low-NA lightingsystem. The system 1100 comprises the Fresnel lens 805, the optional UVand IR filter 810, the negative lens 815, a support base 1105, the solartracker 125, an elevation-adjusted highly reflective mirror 1110, anazimuth-adjusted highly reflective mirror 1115, and the low-NA optimizer130.

On reaching the low-NA lighting system 1100, light enters the Fresnellens 805, which may be used in place of the primary light concentrator105 and the secondary light concentrator 110. On either side of theFresnel lens 805, a UV and IR filter 810 may be placed to filter the UVand IR radiation as described in FIG. 2. More than one Fresnel lens maybe used, but they should all share the same focus point to assure thebest low-NA optimization.

The negative lens 815 is near the focal point of the Fresnel lens tomodify the numerical aperture of the concentrated light 115 as shown inFIG. 8 before reaching the low-NA optimizer 130.

Above and on either side of the entrance to the low-NA optimizer are theat least two highly reflective mirrors, 1110 and 1115. The solar tracker125 adjusts the elevation and azimuth of the highly reflective 1110 and1115 respectively to compensate for the movement of the sun. Highlyreflective mirror 1110 is aligned to the optical axis of the Fresnellens 805. Highly reflective mirror 1115 is aligned to the optical axisof the low-NA optimizer 130. With this continuous adjustment, theelevation and azimuth adjusted highly reflective mirrors 1110 and 1115reflect the incoming light into the low-NA optimizer 130 with littleloss.

Any of the described embodiments of the low-NA optimizers 130, 300, 400,500, or 600 may be used for enjoyment of the low-NA optimized light fromthe low-NA lighting system 1100. Some embodiments of the low-NA lightingsystems may include the diverging refractive lens 410. The transmittedlight from any of the low-NA lighting systems may also be used forheating, cooking, and other applications.

FIG. 12 shows an embodiment 1200 of the one-axis low-NA lighting system.The one-axis low-NA lighting system 1200 comprises the solar tracker125, a primary concentrator 805, a secondary concentrator 1205, at leastone fiber optic bundle 905, the low-NA-optimizer 710, and the lightfixture 135. Some embodiments may comprise an inlet window 1210 and anenclosure 1215.

The primary concentrator 805 may be a Fresnel lens described in FIG. 8.Protecting the primary concentrator 805 may be an inlet cover 1210. Theinlet window 1210 may be constructed of a framed glass or acrylicwindow. Both glass and acrylic windows have good light transmissionwhile providing adequate protection for the system. The UV and IR filter(FIG. 2, 210) “Energy Film” may be attached to the inner surface of thewindow.

The enclosure 1215 provides support to the primary concentrator 805 andthe secondary concentrator 1205 and protects these optical componentsfrom dust, water, wind, and UV radiation. The primary concentrator maybe affixed to the enclosure 1215, which may be fixed to the solartracker 125. The solar tracker 125 operates in the azimuth-tracking modein this embodiment. The elevation angle may be adjustable by changingthe screw location. For year round operation, the primary concentratorshould be tilted by the local solar zenith angle of equinox.

The secondary concentrator 1205 further concentrates the concentratedlight 115 and conducts the concentrated light 115 from the primaryconcentrator to the at least one fiber optic bundle 905. The secondaryconcentrator 1205 may be a compound parabolic concentrator (CPC). Thesecondary concentrator 1205 may be formed of acrylic, which has arefraction index of about 1.46. The acrylic CPC in air is designed to bea total internal reflection (TIR) CPC. The collecting angle (q sub in)of the secondary concentrator should be greater than 23.5 degree or themaximum exit angle of the primary concentrator. This is due to the angleof incidence onto the normal of the CPC, which varies between 23.5degree at the summer solstice and −23.5 degree at the winter solstice.The exit angle (q sub out) of the secondary concentrator is designed tomatch the numerical aperture of the optical fibers. All surfaces of theacrylic CPC, especially both end surfaces, need to be polished. The exitcross section of the CPC should not be bigger than that of the opticalfiber. The CPC with the optical fiber can be made into one piece by theinjection mold technique. An anti-reflection (AR) coating or AR film maybe applied to the entering end surface of the CPC to reduce thereflection loss. Glass, quartz, or other transparent materials may beused in the place of acrylic.

The at least one fiber optic bundle 905 transmits the concentrated lightto the low-NA optimizer 710. The at least one fiber optic bundle 905 aredescribed in FIG. 9. An advantage of an acrylic fiber optic bundle 905is that it may be combined with the secondary concentrator 1205 into onecomponent.

The function and elements comprising the low-NA optimizer 710 aredescribed in FIG. 7. The low-NA optimized light is then conducted to thelight fixture 135 for illumination.

FIG. 13 shows an alternative embodiment 1300 of the one-axis low-NAlighting system. The one-axis low-NA lighting system 1300 comprises thesolar tracker 125, a primary concentrator 1305, a highly reflectivelinear mirror 1310, a secondary concentrator 1205, at least one fiberoptic bundle 905, an aperture 1315, the low-NA optimizer 710, and thelight fixture 135 (not shown).

The primary concentrator 1305 concentrates incoming light as a thin lineof concentrated light 115 to the mirror 1310. The primary concentrator1305 may be a parabolic trough 1305. The primary concentrator may beaffixed to the solar tracker 125. The solar tracker 125 operates in theazimuth-tracking mode in this embodiment. The elevation angle may beadjustable by changing the screw location. For year round operation, theprimary concentrator should be tilted by the local solar zenith angle ofequinox.

The highly reflective linear mirror 1310 reflects the concentrated light115 to the secondary concentrator 1205. The highly reflective linearmirror 1310 may be a flat mirror, a concave reflector, or a convexreflector. The highly reflective linear mirror 1310 should be narrowsince its shadow will block some of the incoming light and cause ashadowing loss of incoming light.

The secondary concentrator 1205 may be a compound parabolic concentratoras described in FIG. 12 to conduct the concentrated light 115 to the atleast one fiber optic bundle 905. The at least one fiber optic bundle905 is described in FIG. 9 for conducting the concentrated light 115 tothe low-NA optimizer 710.

An aperture 1315 through the primary concentrator 1305 may be used withthe at least one fiber optical bundle 905 to transport the concentratedlight 115 to the low-NA optimizer 710. The function and elementscomprising the low-NA optimizer 710 are described in FIG. 7. The low-NAoptimized light is then conducted to the light fixture 135 forillumination (not shown).

FIGS. 14A, 14B, 14C and 14D show an expanded view of a compoundparabolic secondary concentrator. In some embodiments, the secondaryconcentrator may be a circular conical concentrator (FIGS. 14A and 14B).In some embodiments, the secondary concentrator may be a non-circularconical concentrator. The secondary concentrator may be a square conicalconcentrator (FIGS. 14C and 14D).

FIG. 15 shows a flowchart of a method for concentrating natural lightfor interior lighting.

At step 1505, light is received from a natural source.

At step 1510, the light is concentrated with at least two lightconcentrators.

At step 1515, ultraviolet and infrared light is filtered from the light.

At step 1520, the concentrated light is oriented along an optical axisso that the concentrated light has a low numerical aperture within athermodynamic limit.

At step 1525, the low numerical concentrated light is transmitted to alight fixture.

The embodiments discussed here are illustrative of the presentinvention. Elements in the figures are illustrated for simplicity andclarity and are not drawn to scale. Some elements may be exaggerated toimprove the understanding of various embodiments. The descriptions andillustrations, as well as the various modifications or adaptations ofthe methods and/or specific structures described are within the spiritand scope of the present invention. Hence, these descriptions anddrawings should not be considered in a limiting sense, as it isunderstood that the present invention is in no way limited to only theembodiments illustrated.

1. A low numerical aperture system for transmitting light for interiorlighting, comprising: a light tracking system for aligning at least onelight concentrator towards a light source; at least one lightconcentrator for receiving light from the light source, concentratingthe light and directing the concentrated light towards at least onehighly reflective mirror; at least one highly reflective mirror movablyaffixed to a low-NA optimizer and configured to coordinate to a solartracking axis by the light tracking system to reflect the concentratedlight into the low-NA optimizer; and a low-NA optimizer comprising atleast one light guide having at least one optical axis and at least onelight guide mirror such that the low-NA optimizer is configured toorient the concentrated light along the optical axis and to optimize thenumerical aperture of the concentrated light within a thermodynamiclimit and to transmit the low-NA optimized concentrated light forinterior lighting.
 2. The low numerical aperture system for transmittinglight for interior lighting of claim 1 wherein the light tracking systemcomprises at least a one-axis solar tracking system.
 3. The lownumerical aperture system for transmitting light for interior lightingof claim 1 wherein the at least one light concentrator comprises aparabolic reflector and a hyperboloidal reflector.
 4. The low numericalaperture system for transmitting light for interior lighting of claim 1further comprising at least one filter for filtering ultraviolet andinfrared radiation from the light.
 5. The low numerical aperture systemfor transmitting light for interior lighting of claim 1 wherein thelow-NA optimizer further comprises a highly reflective film fororienting concentrated light to a low numerical aperture.
 6. The lownumerical aperture system for transmitting light for interior lightingof claim 1 wherein the low-NA optimizer comprises a diverging refractivelens for modifying the concentrated light to a low numerical aperture.7. The low numerical aperture system for transmitting light for interiorlighting of claim 1 wherein the low-NA optimizer comprises asemi-circular light guide shaped to optimize the numerical aperture ofthe concentrated light.
 8. The low numerical aperture system fortransmitting light for interior lighting of claim 1 wherein the low-NAoptimizer comprises a conic parabolic concentrator for optimizingconcentrated light to a low numerical aperture.
 9. The low numericalaperture system for transmitting light for interior lighting of claim 1wherein the low-NA optimizer comprises a conic exponential concentratorfor optimizing concentrated light to a low numerical aperture.
 10. Thelow numerical aperture system for transmitting light for interiorlighting of claim 1 wherein the low-NA optimizer comprises a reversecompound parabolic concentrator for optimizing concentrated light to alow numerical aperture.
 11. The low numerical aperture system fortransmitting light for interior lighting of claim 1 wherein the low-NAoptimizer comprises a reverse conic exponential concentrator foroptimizing concentrated light to a low numerical aperture.
 12. The lownumerical aperture system for transmitting light for interior lightingof claim 1 wherein the low-NA optimizer comprises a parabolic reflectorfor optimizing concentrated light to a low numerical aperture.
 13. Thelow numerical aperture system for transmitting light for interiorlighting of claim 1 wherein the low-NA optimizer comprises an ellipticalreflector for optimizing concentrated light to a low numerical aperture.14. The low numerical aperture system for transmitting light forinterior lighting of claim 1 wherein the at least one light concentratorcomprises a Fresnel lens for concentrating light.
 15. The low numericalaperture system for transmitting light for interior lighting of claim 14further comprising a diverging refractive lens for modifying theconcentrated light of the light from the at least one lightconcentrator.
 16. The low numerical aperture system for transmittinglight for interior lighting of claim 1 wherein the light source is thesun.
 17. The low numerical aperture system for transmitting light forinterior lighting of claim 1 wherein the light source is artificiallighting.
 18. A method for interior lighting, comprising: receivinglight from a natural source; concentrating the light; filteringultraviolet light and infrared light from the light; orienting theconcentrated light along an optical axis of an low-NA optimizer havingat least one light guide mirror by using a highly reflective mirrorconfigured to coordinate to a solar tracking axis and movably affixed tothe low-NA optimizer so that the concentrated light has a low numericalaperture within a thermodynamic limit; and transmitting the lownumerical aperture concentrated light to a light fixture.